Paperboard is a low-cost material which is ubiquitous in the field of packaging generally. Its strength and thermal insulation properties are however limited, and laminates with other materials have been developed and are widely used. For example, U.S. Pat. Nos. 7,192,640 and 5,091,261 disclose paperboard/polymer laminates for forming blister packs. These patents do not disclose the use of such laminates for making paper cups or other food or beverage containers. U.S. Pat. No. 6,811,843 describes a cup formed from a laminate including an insulating layer and a paper stock layer. The insulating layer is heat-laminated foam formed from high density polyethylene, low density polyethylene, linear low density polyethylene, or oriented polypropylene. U.S. Pat. No. 6,277,454 discloses a single-walled container for storing hot or cold liquids, comprising an inner layer of paperboard laminated to an outer layer of syntactic foam. Void-containing particles in the foam improve the thermal insulation. The syntactic foam outer layer contains void structure and a regular pattern, such as stripes or dots, to improve the thermal insulation.
A single-walled container is known for its limitation of strength, and its vulnerability to damage of the exposed pattern of foam. Since such containers are intended to hold scalding hot liquids, these disadvantages can give rise to product liability issues. A double-walled laminate container is sturdier, but the doubled laminated structure has poor flexibility. Therefore, it is relatively difficult in forming the doubled laminated structure into a container shape using the standard cup-making machines.
Additionally, there has been increased environmental concern for biodegradability and recycling of packaging materials. Synthetic foams and thermosetting plastics are neither biodegradable nor recyclable, and in many cases they produce toxic breakdown products when incinerated. Therefore, the known thermally insulating packaging materials and containers made of paperboard/polymer laminates presents environmental concerns.
Accordingly, there is a need for the biodegradable packaging material with enhanced thermal-insulating performance and strength that allows for its production using the existing papermaking process and for its formation into the packaging containers using the existing converting process, such that an improved cost per package may be achieved and the packaging containers may be formed, filled and sealed at economically high speeds using conventional packaging machine temperatures, pressures and dwell times.